Ion film regulating device

ABSTRACT

Apparatus for regulating liquid film thickness are provided. The apparatus provided by the present invention comprises: AN ELONGATED CORONA DISCHARGE ELECTRODE; A CORONA GENERATING POTENTIAL SOURCE CONNECTED TO SAID DISCHARGE ELECTRODE ADAPTED TO APPLY A CORONA GENERATING POTENTIAL BETWEEN SAID DISCHARGE ELECTRODE AND A GROUND ELECTRODE; MEANS ADAPTED TO OVERCOAT A SURFACE WITH A NON-CONDUCTIVE LIQUID FILM; AND MEANS ADAPTED TO ESTABLISH RELATIVE MOTION BETWEEN SAID DISCHARGE ELECTRODE AND THE OVERCOATED SURFACE IN CLOSE SPACED RELATION TO SAID DISCHARGE ELECTRODE, WHEREBY SAID DISCHARGE ELECTRODE CREATES AN ION CURTAIN EXTENDING ACROSS THE PATH OF RELATIVE MOVEMENT OF THE SURFACE AND THE DISCHARGE ELECTRODE WHICH IMPINGES UPON SAID NON-CONDUCTIVE LIQUID FILM, AND, UPON RELATIVE MOVEMENT OF SAID SURFACE AND SAID DISCHARGE ELECTRODE, WIPES AT LEAST THE PORTION OF SAID FILM FROM SAID SURFACE.

United States Patent 1 1 1111 83,826

'Urbanek et al. I [4 Jan. 8, 1974 ION FILM REGULATING DEVICE Primary ExaminerMervin Stein [75] Inventors. Edwin A Ur-bmk Assistant Examiner-Leo Millstein Rich! vock mario both of Attorney-James J. Ralabate et a1.

N.Y. I

[73] Assignee: Xerox Corporation, Rochester, NY. ABSTRACT [22] Filed: Aug. 20, 1971 Apparatus for regulating liquid film thickness are pro vided. The apparatus provided by the present invention comprises:

an elongated corona discharge electrode;

[21] App]. No.: 173,583

[52] US. Cl 118/620, 96/1, 117/93.4, a corona generating potential source connected to 118/637, 355/3, 355/10 said discharge electrode adapted to apply a [51] Int. Cl G03g 13/00, B050 5/00 corona generating potential between said [58] Field of Search 1 18149.1, 49.5, 50.1, discharge electrode and a ground electrode;

118/620, 104, 637; ll7/93.1 CD, 93.4 R, means adapted to overcoat a surface with a 111 R; 96/1 E, 1 D; 355/3, 10; 250/495 ZC non-conductive liquid fi1m; and

v means adapted to establish relative motion between [56] References Cited said discharge electrode and the overcoated UNITED STATES PATENTS surface in close spaced relation to said discharge 3,411,482 11/1968 Brodie 118/637 electwde .whereby. Said discharge electrode 3,169,886 4 2/1965 Simm 8/637 creates an ion curtain extending across the path 3,274,089 9/1966 Wolinski 204/165 of relative movement 0f the Surface and the 3,433,374 12/1969 Erben 250/495 discharge electrode which p g p Said 3,263,649 8/1966 Heyletal. 118/637 non-conductive liquid film, and, upon relative 3,250,638 5/1966 Lassiter 117/47 movement of said surface and said discharge 3,639,049 2/1972 Rhodes et al. 355/3 electrode wipes at least the portion of said from said surface.

ION FILM REGULATING DEVICE This invention relates to regulating the thickness r liquid films on a surface. More particularly, this invention relates to the use of an ion curtain to regulate or remove a liquid non-conductive film from a surface.

it man rbibdiiiiihEJ665635, a start magi;

particles have been established upon the copy sheet in image configuration, the insulating medium is surplusage and must be removed. Heretofore, these problems of film thickness control and removal have been solved by an assemblage of a variety of doctor blades, squeegees, heaters and the like clustered about the reproduc tion apparatus. Then too, these metering devices required frequent cleaning necessitating periodic withdrawal of the equipment from use for servicing.

""ii'i readil /5,5555% that a device which could provide fast, efficient and uniform film thickness control and could also be employed for complete removal of liquid films without disruption of the formed image would be highly desirable.

ita'esr'aiiagiwi is ano'bj ect br'niapre' em invention to provide a device which overcomes the above-noted deficiencies.

iii;a'iia'mrbbja to provide a device which provides fast, efficient and uniform film thickness control. lt is" mira'aanie'r as e'c'i'ts'mwae a device for 6.551 plete removal of liquid films from a surface without disruption of any image formed on said surface.

his a still fame-F05 2; "a? the pta irfifivaiaaa to provide a device which accomplishes the above without the need for cleaning.-

"16 another embodiment of the present invention, a device is provided for regulating liquid film thickness by completely or partially removing a liquid from a surface overcoated with a film of non-conductive liquid which comprises:

an elongated corona discharge electrode comprising at least one conductive strand; L

a corona-generating potential source connected to said discharge electrode adapted to apply a corona generating potential between said discharge electrode and a ground electrode;

means adapted to overcoat a surface with a non-- conductive liquid film; and

means adapted to establish relative motion between said discharge electrode and the overcoated surface in close spaced relation to said discharge electrode whereby said discharge electrode creates an ion curtain extending across the path of relative movement of said surface and said discharge electrode which impinges upon said non-conductive film, and, upon relative movement of said surface and said discharge electrode, wipes at least a portion of said film from said surface.

The present invention includes embodiments in which the overcoated surface moves relativeto a stationary corona discharge electrode, or the corona discharge electrode moves relative to the overcoated surface or both the overcoated surface and the corona discharge electrode moves relative to each other. An embodiment which is particularly suitable for photoelectrophoretic imaging systems wherein the overcoated surface will move relative to a stationary corona discharge electrode comprises:

a movable conductive surface adapted to move at a substantially constant speed in a plane parallel to said surface, said surface being maintained at a'reference potential;

means for applying a liquid non-conductive film upon said surface;

an elongated corona discharge electrode comprising at least one conductive strand in spaced parallel relation to said plane extending across the path of movement of said surface; and

a corona-generating potential source connected to said discharge electrode adapted to apply a corona generating potential between said corona electrode and said surface, whereby said corona discharge creates an ion curtain, extending across the path of relative movement of said surface and said electrode which impinges upon said non-conductive film and, upon relative movement of said surface and said corona discharge electrode, wipes at least a portion of said film from said surface.

For purposes of illustrationonly, the present invention will be described with reference to its application to photoelectrophoretic imaging systems. It should be apparent, however, that the present invention is applicable with equal facility to liquid development reproduction systems such as electrophoretic imaging. Also, the present invention can be employed in any instance where a non-conductive liquid film is being applied to O a surface. Thus, it can be employed for regulation of film thickness when, for example, a zinc oxide binder layer is being applied to a backing support. Other applications of the present invention will be readily apparent imaging suspensionis comprised of light sensitive particles suspended within an insulating liquid carrier and believed to bear a net electricalcharge while in suspension. Normally, the suspension is placed between inv jecting and blocking electrodes used to establish an electric field of essentially constant magnitude and is exposed to a variable light image through one of the electrodes which is at least partially transparent. According to one theory, particles attracted to the injecting electrode by the electric field exchange charge. with the injecting electrode when exposed to light and migrate under the influence of the field through the liquid carrier to the blocking electrode. As a result of the migration, positive and negative images are formed on the two electrodes. The blocking electrode is a conductive core covered with a dielectric material to prevent charge exchange with the particles and thereby prevent the particles from oscillating back and forth between the two electrodes.

Photoelectrophoretic imaging processes can be either monochromatic or polychromatic depending upon whether the light sensitive particles within the liquid carrier are responsive to the same or different portions of the visible spectrum. A full color polychromatic system can be obtained, for example, by using cyan, magenta and yellow colored particles which are responsive to red, green and blue light respectively. In a monochromatic system, the particles included in the imaging suspension can be virtually any color in which it is desired to produce the final image and the particular point or range of its spectral response is relatively immaterial as long as it can be matched by a convenient exposure source. In fact, in a monochromatic system, the pigment can vary in response from one with a very narrow response band to one having panchromatic response. In polychromatic systems, however, the particles are generally selected so that particles of different colors respond to different wavelengths in the visible spectrum, thus allowing for color separation.

An extensive and detailed description of the photoelectrophoretic process is found in U.S. Pat. Nos. 3,384,565 and 3,384,484 to Tulagin and Carreira, U.S. Pat. No. 3,383,993 to Yeh and 3,384,566 to Clark. The disclosures contained in these patents are expressly incorporated by reference into the present disclosure.

The present invention will become more apparent upon consideration of the following detailed disclosure of the invention, especially when taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a schematic representation of a continuous photoelectrophoretic duplicator wherein the device of the present invention is employed to regulate the thickness of the imaging suspension prior to entering the imaging zone;

FIG. 2 is a schematic representation of a continuous photoelectrophoretic duplicator wherein the device of the present invention is employed to remove the insulating carrier liquid from the transfer web after formation of the image thereon; and,

FIG. 3 is a schematic representation of a continuous polychromatic photoelectrophoretic duplicator wherein the device of the present invention is employed to remove the insulating carrier liquid from the transfer web after formation of an image thereon.

Referring now to FIG. 1, there is seen a continuous photoelectrophoretic duplicator comprising transparent injecting electrode 1 and blocking electrode 10. The injecting electrode 1, in the instant illustration, is represented as consisting of a layer of optically transparent glass 2 overcoated with a thin optically transparent layer of tin oxide 3. Tin oxide coated glass of this nature is commercially available under the trade name NESA glass. A layer of an imaging suspension is coated on the surface of the transparent injecting electrode by an applicator 6 of any suitable design or material, suchas a urethane coated cylinder, which may rotate in the same direction or, as herein represented, in the opposing direction to the transparent cylinder. The function of the ink applicator is to apply a thin film of the imaging suspension from ink sump 7 by way of roller 8 to the transparent cylinder. In close proximity to the transparent roller electrode 1 is a second rotary blocking electrode 10 having a conductive central core 11 which is covered with a layer of material 12 the function of which is to block the rapid exchange of electric charges between the particles, and the elecuse of such a layer is preferred because of the markedly improved results which it is capable of producing. A

' detailed description of the improved results and the types of materials which may be employed as the blocking layer may be found in U.S. Pat. No. 3,383,993. The imaging suspension generally consists of a dispersion of photosensitive pigment particles in an insulating carrier liquid or vehicle.

A receiver sheet 13 is driven between cylinders l and 10 as represented, with an ink image selectively deposited on the receiver sheet in the imaging zone. A residual image pattern opposite in image sense to the image developed on the receiver sheet is formed on the NESA glass cylinder which is removed at the ink application station. Thus the applicator performs both the ink application and residual image removal steps.

As the imaging suspension 5 on the injecting electrode 1 rotates toward the imaging zone formed in the nip between the injecting electrode '1 and the blocking electrode 10, it passes under corona discharge electrode 20 from which emanates an ion curtain 22 which impinges upon said imaging suspension and wipes at least a portion of said suspension from the surface of the injecting electrode l thereby regulating the thickness of the film of imaging suspension entering the imaging zone. It will be understood that the degree of film removal is inversely proportional to lineal velocity of overcoated surface relative to the corona discharge electrode. Velocities of 0.5 to 6 in/sec are generally considered preferable for use in the present invention, with lower velocities being needed to effect more complete removal of highly viscose liquid coatings.

When a high voltage is applied to a fine wire, point or edge, a corona discharge may be formed, which sprays ions of the same polarity as the wire to nearby objects at lower potentials. The mechanism bywhich the ions are formed is not completely understood, and it differs for positive and negative corona, but in both, electron avalanches play an important part.

Ina negative corona discharge, the field around the wire causes the positive ions always present in the air (produced by cosmic rays, etc.) to move toward the wire, where, by impact, some of them produce electrons. In the region of high field strength near the wire, the electrons are accelerated to high enough energies that some of their collisions with air molecules produce additional electrons and positive ions. These electrons in turn are accelerated and have ionizingcollisions in an electron avalanche, which proceeds outward from the wire until the field strength drops below the value which will produce ionizing collisions. The electrons continue to move away from the wire, most of them attaching themselves to oxygen molecules, to form the observed spray of negative ions. Meanwhile, the positive ions produced drift toward the wire. BEcause they are less mobile than the electrons, they form a positive space charge around the wire, which partially quenches the discharge by reducing the field strength. On reaching the wire, they produce more electrons and more avalanches, and the discharge is maintained. Negative corona is thus a pulsating or intermittent type of discharge. Also, because the efficiency with which electrons are produced by positive-ion bombardment depends on characteristics of the electrode (work func tion, contamination, temperature, and others) the discharge will be irregularly distributed over the surface. In the case of a fine wire, the discharge will appear as a series of active areas hot spots strung out more or less uniformly along the wire.

In a positive corona discharge, the field around the wire causes nearby electrons (again produced by cosmic rays,etc.) to accelerate toward the wire. Near the wire, electron avalanches are formed. Positive ions produced by the collisions in these avalanches mvoe away from the wire and through the'air toward objects at lower potentials. To maintain the discharge, there must be a source of electrons in the region surrounding the wire. This source is chiefly ionization occurring when photons produced in the glow accompanying the corona discharge are absorbed by nearby air molecules. Due to the avalanche nature of the discharge, positive corona is somewhat pulsating in character, but because the region where positive ion space charge exists is'not so sharply defined, positive corona is smoother than negative. Also, since the source of electrons is gas molecules that have uniform ionization characteristics and are uniformly distributed around the wire, the discharge is uniform over its surface.

6 ation the NESA glass injecting electrode is connected to group. The receiver sheet 13 herein represented in the form of a paper web is fed from a supply roll 36 This spray or avalanche of ions which emanates from the corona discharge electrode and rains or cascades down impinging upon the liquid imaging suspension is referred to herein and in the appended claims as an ion curtain. It has been found in the present invencorona discharge electrode and the injecting electrode forming a rolling bank 24 of excess suspension which has been wiped from the surface of theelectrode. This rolling bank has been found to form on the surface of the injecting electrode at a point just behind the corona discharge electrode in the direction of rotation.

The extent to which the ion curtain can effect film thickness regualtion will depend primarily upon how insulating the carrier liquid is, the viscosity of the liquid, the spacing of the corona discharge electrode from the injecting electrode surface, the magnitude of the potential applied to the corona discharge electrode and the rate of rotation of the rotary electrodes. Generally, the mostconvenient manner of effecting film thickness control is by varying the potential applied to the corona discharge electrode since, in a commercial operation, the interelectrode spacing an the nature of the imaging suspension will'usually be fixed Thus, by employing a power source 26 adapted to supply to the corona-discharge electrode 20a potential which can be easily varied, film thickness control can readily be effectedlt is apaprent, of course, that as theapplied potential is increased, the film thickness will decrease until, in the ul-' timate, it will be completely removed. Thus, the device of the present invention can be employed'for both film thickness control and solvent removal. Generally, 'potentials ranging from about 3.8 KV volts to about 10 KV volts are considered suitable for use in the present invention, with the higher potentials being required to effect solvent removal.

As the uniformly thin film of imaging suspension enters the imaging zone between the injecting and blocking electrodes, an image is projected into the nip of the rollers by way of a first surface mirror designated 39 while a field is established across the imaging zone as the result of power source Through the entire operpassing between the transparent injecting electrode and the blocking electrode and is rewound on take up roller 37. A heated metallic shoe 38 in contact with the underside of the paper web can be employed to supply the energy for fixing.

A wide range of voltages may be applied between the electrodes in the system at which imaging occurs. It is preferred in order to obtain good image resolution that the potential be such as to create an electric field of at least about volts per micron across the imaging layer. The applied potential necessary to obtain the desired field strength will of course vary depending upon the interelectrode gap and upon the thickness and type of blocking material used on the respective imaging electrode surface. Voltages as high as 8,000 volts have been applied to produce images of high quality. The upper limit of the field strength is limited only by the breakdown potential of the suspension and blocking electrode material.

Imaging as carried out in conjunction with the present invention will generally be in a negative to positive or positive to negative imaging mode. Thus, for purposes of the present discussion in order to produce the positive image on the receiver sheet a negative image is projected into the nip onto the imaging suspension. As discussed above, a potential is applied across the imaging suspension and, as a result of the exposure to the actinic radiation, the exposed pigment particles initially suspended in the carrier liquid migrate through the car-;

rier to the surface of the blocking electrode or, in the instance of the above described illustration,-'to the surface of the intervening receiver paper sheet. The pigment image formed, whether it be on a removable blocking electrode layer attached to the conductive core of the imaging roller or to a receiver copy sheet may be fixed in place, for example, by placing a lamination over its top surface such as by spraying with a thermoplastic composition-or by the application of heat such as by the utilization of a heated metallic shoe which is in contact with the underside of the paper web as in the present illustration. When afusible polymeric material such as a thermoplastic resin is utilized in conjunction with the pigment'particles, the system presents a built-in image fixing mechanismwhen utilizing heat fixing or vapor fixing techniques. In addition, the application of heat further assists in the fixing process by accelerating the solvent removal from the image areas. If desired, the image may be transferred to a secondary substrate to which it is in turn fixed. I

If the image is formed on a permanent electrode su'r-. face, and the intervening receiver sheet is eliminated, it will be found desirable to transfer the image from the electrode and fix it on a secondary substrate-sothat the electrode may be reused. Such a transfer step may be carried out by adhesive pick off techniques or preferably by electrostatic field transfer. If the blocking electrode is covered with a transfer paper sleeve or as illustrated a web is passed between the contacting surfaces of the injecting and blocking rollers or if the blocking material utilized consists of a removable sleeve, such as Tedlar, this intervening substrate will pick up the complete image on the initial pass and need only be removed to produce the final usable copy. All that is required is to replace the substrate with a similar material. In the present configuration images are produced directly on a paper receiving sheet or other substrate with the image formed on the NESA or transparent cylinder removed by the action of the ink applicator. However, if desired, the image formed on the NESA cylinder need not be discarded but may be utilized by offsetting the image from the NESA cylinder onto the surface of a conventional receiving sheet such as described above. Any suitable material may be used as the receiving substrate for the image produced such as paper as represented in the illustration or other desirable substrates. For example, if one desires to prepare a transparency the use of a Mylar or Tedlar sheet might be desirable.

When used in the course of the present invention, the term injecting electrode should be understood to mean that it is an electrode which will preferably be capable of exchanging charge with the photosensitive particles of the imaging suspension when the suspension is exposed to light so as to allow for a net change in the charge polarity on the particle. By the term blocking electrode is meant one which is capable of injecting the electrons into or receiving electrons from the above mentioned photosensitive particles at a negligible rate when the particles come into contact with the surface of the electrode.

It is preferred that the injecting electrode be composed of an optically transparent material, such as glass, overcoated with a transparent or semitransparent conductive material such as tin oxide, indium oxide, copper iodide, aluminum or the like; however, other suitable materials including many semiconductive materials such as raw cellophane, which are ordinarily not thought ofas being conductors but which are still capable of accepting injected charge carriers of the proper.

polarity under the influence of an applied electric field may be used. The use of more conductive materials allows for cleaner charge separation and prevents possible charge buildup on the electrode, the latter tending to diminish the electric field across the suspension in an undesirable manner.

The blocking electrode, on the other hand, is selected so as to prevent or greatly retard the injection of electrons into the photosensitive pigment particles when the particles reach the surface of this electrode. The core of the blocking electrode generally will consist of a material which is fairly high in electrical conductivity. Typical conductive materials include conductive rubber, steel, aluminum, copper and brass. Preferably, the core of the electrode will have a high electrical conductiveity in order to establish the required polarity differential in the system however, if a material having a low conductivity is used, a separate electrical connection may be made to the back of the blocking layer of the blocking electrode. For example, the blocking layer or sleeve may be a semiconductive polyurethane material having a conductivity of from about to 10 ohm-cm. If a hard rubber nonconductive core is used, then a metal foil may be used as a backing for the blocking sleeve. Although a blocking electrode material need not necessarily be used in the system. the use of such a layer is preferred because of the markedly improved results which it is capable of producing. It is preferred that the blocking layer, when used, be either an insulator or a semiconductor which will not allow for the passage of sufficient charge carriers, under the influence of the applied field, to discharge the particles finely bound to its surface thereby preventing particle oscillation in the system. The result is enhanced image density and resolution. Even if the blocking layer does allow for the passage of some charge carriers to the photosensitive particles, it still will be considered to fall within the. class of preferred materials if it does not allow for the passage of 'sufficient charge so as to recharge the particles to the opposite polarity. Exemplary of the preferred blockin gmaterials used are baryta paper, Tedlar a polyvinylfluoride, Mylar (polyethylene terephthalate), and polyurethane. Any other suitable material having resistivity of from about 10 ohms-cm. or greater may be employed. Typical materials in this resistivity range include cellulose acetate coated papers, cellophane, polystyrene and polytetrafluoroethylene. Other materials that may be used in the injecting and blocking electrodes and other photosensitive particles which can be used as the photomigratory pigments and the various conditions under which the system operates may be found in the above cited issued patents U.S. Pat. Nos. 3,384,565 and 3,384,566 as well as U.S. Pat. Nos. 3,384,488 and 3,389,993.

lt is to be understood that any suitable combination of photosensitive pigments may be employed within the course of-the present invention with the selection depending largely upon the effect desired in the final image. Typical photoresponsive materials include substituted and unsubstituted organic pigments such as phthalocyanines such as Monarch Blue G beta crystal line form of copper phthalocyanine available from Hercules, lnc.,- quinacridones such as, Monastral Red B quinacridone pigment available from duPont, Algol Yellow G.C. l,2,5,6-di (C,C'-diphenyl)- thiazoleanthraquinone) (CI. 67300), ,lragazine ,Red, tri-sodium salt of 2-carboxylphenylazo 2-naphthol-3,6- disulfonic acid-OI. 16105), N-2-pyridyl-8,l3- dioxodinaphtho (l,2-2',3)-furan-6-carboxamide, 3- aminocarbazole, Watchung Red B (the barium salt of l-( 4-methyl-5 '-chloroazobenzene-2'-sulfonic acid )-2- hydroxy-3-naphthoic acid-C.l. 15865); and inorganic pigments such as cadmium sulfide, cadmium selenide, selenium sulfide, antimony sulfide, zinc oxide, and ar-' senic sulfide. A more complete list of suitable photosensitive pigments is described in U.S. Pat. No. 3,384,488.

Any suitable insulating carrier liquid may be used in the course of the present invention. Typical vehicles include decane, dodecane, tetradecane, Sohio Solvent 3454, a kerosene fraction available from Standard Oil Company of Ohio, dimethylsiloxane, olive oil, linseed oil, mineral oil, cottonseed oil, marine oils such as sperm oil and cod liver oil and mixtures thereof.

Referring now to FIG. 2, there is shown an alternate embodiment of the present invention wherein like immerals identify like components as shown in FIG. 1. In this embodiment, once the suspension particles are deposited upon the transfer web 13 in image. configuration, the residual insulating carrier liquid is removed from the web, without affecting the image, by passage between corona discharge electrode 40 and conductive plate 42 which is connected to ground potential. Corona discharge electrode 40 is connected to a DC. or biased A. C. power source 44 which is adapted to apply a corona generating potential between said corona dis charge electrode 40 and said plate 42. In this manner, an ion curtain is generated which impinges upon the transfer web 13 passing therebetween. The potential applied to the corona discharge electrode is of sufficient magnitude to create a high intensity ion curtain which will effectively force the non-conducting carrier liquid away from the direction of movement of the transfer web 13, thereby removing the liquid from the web, as if said liquid was squeegeed off the web, without disruption of the image. The liquid which is removed forms a rolling bank or liquid bead 46 behind the corona discharge electrode.

If desired, although it is not considered necessary, a heated metallic shoe (not shown) can be employed in contact with the underside of the transfer web at a point beyond the corona discharge electrode to supply the energy needed for fixing the image to the web. The use of such a heated shoe may be useful when a fusible polymeric material such as a thermoplastic resin is employed in conjunction with the pigment particles in the imaging suspension.

FIG. 3 illustrates an embodiment of the invention employed in a polychromatic photoelectrophoretic duplicator. The embodiment of FIG. 3 removes residual insulating liquid from a transfer web as was described with respect to FIG. 2 and those elements of FIG. 3 performing the same functions as elements of FIG. 2 bear the same reference numerals. The inking material 5 in this arrangement comprises a mixture of color pigments as for example magneta, cyan and yellow in an insulating liquid. An injector electrode 1 is coated with this ink and is exposed to a color image subject via the mirror 39. The color image is formed by a subtractive color technique wherein a negative color image is initially transferred by the photoelectrophoretic process to the surface of the blocking electrode 12 and the positive color image remaining on the injector electrode 1 is then transferred to the web 13. Those pigmented particles which are transferred to the blocking electrode are removed therefrom during clockwise rotation of this electrode by a doctor blade 60 and a rotating brush 62. The positive color image remaining on the injecting electrode is transferred to the web 13 by pressure contact with the web. This transfer is enhanced by establishing a charge on the web 13. A charge can be established on the web 13 by a corotron 64. A roller 66 is shown positioned at the junction of the web and surface of the injecting electrode and forces the web into contact with the surface of the blocking electrode. The residual insulating liquid is then removed from the web by the ion curtain as described hereinbefore with respect to FIG. 2. A particularadvantage of this method of liquid removal is the removal of oil while avoiding displacement of the color pigments. Further, the bond between the pigments and the transfer web is strengthened.

Although the present invention has been illustrated with reference to photoelectrophoretic imaging systerns, it is equally applicable to any system wherein a non-conductive liquid film is applied to a conductive surface or to an insulating web upon a conductive surface. As illustrated above, the present invention can be employed for film thickness control or for liquid film application or removal. Any continuous area of higher relief could be coated selectively due to closer spacing, higher current, stronger fields and surface tension characteristics. It should be apparent-that once a rolling bank or liquid bead is established behind the corona discharge electrode, it can serve as a means of supplying the liquid for application to the substrate surface as a film with the corona discharge electrode of the present invention acting as a metering and spreading device. In this manner, uniform films can be coated on substrate surfaces. This technique is useful, for example, for applying a film or layer of an organic or inorganic photoconductor optionally in a binder material to a supporting substrate surface.

Although the corona discharge electrode has been illustrated herein as a corotron device of the type described in U.S. Pat. No. 2,836,725 to R. G. Vyverberg, the corona discharge electrode of the present invention can also be of the scorotron type described in U.S. Pat. No. 2,777,957 to LB. Walkup. In addition to the corona-emitting wires and the shield or backing-plate found in a corotron unit, the scorotron contains a grid of parallel wires spaced below the corona-emitting wires and operated at a selected potential between zero and several hundred volts, depending upon the desired intensity of the ion curtain. This screen-controlled device produces a very uniform and controlled ion curtain, because of the action of the screen in suppressing the electric-field between the corona wires and the conductive surface. Scorotron units can be employed advantageously when it is critical that a film of extremely uniform thickness be obtained. A

Other modifications and areas of application of the present invention will occur to those skilled in the art upon a reading of the present disclosure. These are intended to be included within the scope of this invention.

What is claimed is:

1. Apparatus for regulating thickness of a nonconductive liquid film comprising in combination:

a. a cylindrical surface adapted to support a layer of non-conductive liquid film;

b. a first station including coating means to coat a layer of non-conductive liquid film to said surface located at said first station;

c. a second station including a corona discharge electrode fixedly located at a second station which will produce an ion curtain which impinges upon a layer of non-conductive liquid film between the corona discharge electrode and a ground electrode when a corona generating potential is applied across the two electrodes, the 'corona discharge electrode comprising at least one conductive strand positioned in close spatial relationship with said surface;

d. a third station including imaging means located at said third station;

e. means to rotate said surface in a continuous path of travel through said first station adjacent a lowermost portion of its path of travel; then through said second station on an upper quadrant not beyond the uppermost portion of its path of travel; then through said third station, the rate of motion of said surface, and the distance between said corona discharge electrode being sufficient to provide an ion curtain which impinges upon the layer of nonconductive liquid film which wipes only a portion of the layer of non-conductive liquid film from said surface'and permits a predetermined quantity of liquid film to pass to the imaging means and cooperate with the forces of gravity to preclude excess liquid film to pass thereby. 

1. Apparatus for regulating thickness of a non-conductive liquid film comprising in combination: a. a cylindrical surface adapted to support a layer of nonconductive liquid film; b. a first station including coating means to coat a layer of non-conductive liquid film to said surface located at said first station; c. a second station including a corona discharge electrode fixedly located at a second station which will produce an ion curtain which impinges upon a layer of non-conductive liquid film between the corona discharge electrode and a ground electrode when a corona generating potential is applied across the two electrodes, the corona discharge electrode comprising at least one conductive strand positioned in close spatial relationship with said surface; d. a third station including imaging means located at said third station; e. means to rotate said surface in a continuous path of travel through saId first station adjacent a lowermost portion of its path of travel; then through said second station on an upper quadrant not beyond the uppermost portion of its path of travel; then through said third station, the rate of motion of said surface, and the distance between said corona discharge electrode being sufficient to provide an ion curtain which impinges upon the layer of non-conductive liquid film which wipes only a portion of the layer of non-conductive liquid film from said surface and permits a predetermined quantity of liquid film to pass to the imaging means and cooperate with the forces of gravity to preclude excess liquid film to pass thereby. 